1. Field of the Invention
This invention is in the field of apparatus and methods for removing cooking fumes from restaurants, and particularly relates to such apparatus which does not deplete the restaurant of undesirable amounts of air.
2. Description of Prior Art
It is of extreme importance in modern-type exhaust hoods and canopies that the velocity (feet per minute) of flow of air and fumes through the grease-filter means be substantially uniform across the entire "width" (length) of the apparatus. One major reason for this is that there is a particular range of velocities which achieves optimum filtration of grease by combination centrifugal and impingement grease filters such as (for example) are described in the cited U.S. Pat. No. 3,566,585.
To achieve such substantially uniform flow velocity through the grease filters, across the width of the apparatus, the velocity of the supply air delivered to the grease filters should be substantially uniform across the width of the apparatus, and the velocity of air and fumes drawn through the filters (from the exhaust side) should be substantially uniform across the width of the apparatus. It is emphasized that the supply and exhaust velocities are not independent of each other, since the supply velocity is one major factor which regulates exhaust velocity. (It might be thought that supply velocity is automatically equal to exhaust velocity but this is not necessarily so for various reasons, one of which is that much supply air deflects off the grease filters).
The achievement of such uniform velocities should be effected with few parts, at minimum cost, and with a minimum of surfaces which may collect grease on the exhaust side of the apparatus. Also, in many installations, it should be accomplished with "low profile" equipment, by which it is meant that plenums and/or ducts should not project up an unsightly distance above the roof or ceiling of the building.
The problem of achieving uniform velocity is greatly exacerbated when the apparatus is very "wide" (long), such as fifteen, twenty or more feet. To achieve relatively uniform velocities despite such widths, with only one supply duct and one exhaust duct, and with a minimum of parts, height, and grease-collecting regions, constitutes a major advance in the art.
Reference is made to my prior U.S. Pat. No. 3,664,255, which shows in FIG. 3 a series of deflectors 39 intended to achieve uniformity of supply or inlet flow. The present invention achieves substantial uniformity without such deflectors 39, even in apparatus much "wider" (longer) than that specifically shown in the U.S. Pat. No. 3,664,255.
The exhaust apparatus shown in FIG. 4 of the U.S. Pat. No. 3,664,255 does not achieve substantially uniform exhaust velocities in "wide" (long) hoods, for example of the sizes above noted. This major problem was solved, relative to the exhaust side of the apparatus, by the "extended plenum" apparatus described at length in the cited parent patent application Ser. No. 509,555. However, a problem remained relative to excessive height on some very wide installations, which problem generated the solution shown in FIG. 8 of such parent patent application (FIG. 2 of the present application). Such construction of FIG. 8 is intended to replace the vastly more expensive double systems previously used (more than one year prior to the filing date of the present application), and shown (for example) by FIG. 6 of such parent application. FIG. 8 of said parent application is clearly not prior art relative to the present application, in that the construction shown thereby has not yet been marketed, etc.
Reference is also made to the following two approaches (both of which were employed in the prior art): (a) adjusting the filters differently (for greater or lesser flow) at different points across the width of the apparatus, and (b) placing screens or baffles or the like in the plenum adjacent the filters or in connecting ducts. Approach (a) (which has been employed by prior-art workers in conjunction with the filters of the above-cited U.S. Pat. No. 3,566,585) is unsatisfactory in that the adjustment impairs filtration in certain regions, and in that the filters may be incorrectly rearranged after cleaning. Approach (b) (also in the prior art) is unsatisfactory for reasons including the fact that the screens plug up with grease, and baffles (unless employed in an extended plenum as described in the present application) collect grease excessively and/or do not do the job satisfactorily. Reference is made to the above-cited U.S. Pat. No. 3,664,255 at column 5, lines 24 et seq. wherein baffles are mentioned.